Mobile IP is a protocol that allows laptop computer or other mobile units to roam between various sub-networks at various locations while maintaining internet connectivity. The mobile units are often referred to as mobile nodes. Without mobile IP or a related protocol, a mobile node would be unable to stay connected while roaming through various sub-networks. This is because the IP address required for any node to communicate over the internet is location specific. Each IP address has a field that specifies the particular sub-network on which the node resides. If a user desires to take a computer that is normally attached to one node and roam with it so that it passes through different sub-networks, it cannot use its home base IP address. As a result, a business person traveling across the country cannot roam with his or her computer across geographically disparate network segments or wireless nodes while remaining connected over the internet.
To address this problem, the Mobile IP protocol has been developed and implemented. One implementation of mobile IP is described in RFC 2002 of the Network Working Group, which is incorporated herein by reference. The Mobile IP protocol involves the use of one or more foreign agents and a home agent. The home agent is usually a router that is essentially the mobile node's “home base” and is the location to which IP traffic is directed. A foreign agent is also often a router through which a mobile node can connect to the home agent. Although mobile IP in its current form is used mainly as a connection from a foreign agent to a home agent, many service providers are deploying home agents as a way to aggregate their internal networks.